Rainbow Vent Field

[3][4] Located 370 km (229.91 mi) southeast of Faial Island, it is a popular geochemical sampling and modeling site due to close proximity to the Azores and definitive representation of serpentinization from hydrothermal circulation and synthesis.

[6] As a hot, ultramafic-hosted vent field, pH levels of fluids are extremely low with much H2 and CH4 generated from water interactions with mafic igneous rocks.

Remotely Operated Vehicles (ROVs), submersibles, and Conductivity Temperature Depth (CTD) probes have been deployed to sample, characterize, and explore the vent field.

Serpentinization reactions occur with hydrothermal circulation causing water to react with hot iron-containing minerals, releasing H2 gas and transforming the base rock.

Waters circulating deep within Rainbow rise to a high enough pressure or temperature so that they react with the rock and chemical constituents are dissolved into or precipitate out of the vent fluid.

At Rainbow, phase separation is a suggested cause for particularly high concentrations of chloride, trace elements, and hydronium, as they differ greatly from similar MAR vents like Logatchev.

[9] Due to the extreme endmember pH, chloride is hypothesized to act as a dominant cation and therefore forms many weak complexes with other elements at high temperatures.

[28] Due to the hot temperatures, low pH, and longevity of the vent activity, there is a strong case for life to originate at sites similar to the Rainbow Massif.

[25] Regarding macrofauna, the Rainbow Massif has been supportive of many kinds of decapods and mollusks, such as Alvinocarididae and Bathymodiolus respectively, feeding where nutrient-rich vent fluids interact with the cold bathypelagic waters.

Due to its significance as an accessible and examplar ultramafic system, Rainbow is a very popular site for scientific expeditions involving intrusive long-term monitoring, environmental manipulation, and geological sampling.

Rainbow has a tricky history regarding preservation, as the site is within the OSPAR Maritime Area and just outside of Portugal's exclusive economic zone similarly to another vent field, Saldanha.

[31] Portugal was unable to distinguish Rainbow as residing off of the extended Azores shelf region - therefore rendering it unqualified for OSPAR protection as a High Seas location.

A map of the Azores triple junction. In this image, Rainbow is at 36° 14' N and 34° 5' W.
ROV JASON , operated by Woods Hole Oceanographic Institution .
An example of phases for a material. When vent fluids reach a high enough temperature, they may become gaseous and lose chlorine before leaving through a vent chimney.
An example of shrimp, crabs and mussels that could be at the Rainbow Vent field.